Ah, that's helpful. So if I wanted to make a defense station, say, parked next a jump entry point, I would essentially just create a large, engine-less ship? How does that work with maintenance and service time etc. ?
You can also take another approach. Build one or more stations with very long maintenance life. Say, 10 years? Tow them with a tug to the place you want to defend (say a jump point), and when needed (in the example, every 10 years or so) tow it back to your planet and conduct maintenance.
This works best if you make 3-4 such stations, as you can perform maintenance one at a time and still have the others at the jump point. Now, you can always do this for RP, but is it worth doing? Depends
Sensor stations: super useful, build them super minimal and dirty cheap and with very long maintentance life. They'll see anyone who passes through (very useful since in c#aurora sensors have less range). No need to put them ON the jump point, jut park them nearby and in sensor range. I put these on any sort-of-important jump point.
Beam stations: not worth it because of how jump transit works, and because of the limited range of beam weapons
Missile stations: Quite nice for defence. Once again, no need to put them ON the jump point. Some millions km away are perfectly fine
"Carrier" stations: Hell yes I love these. Fill them up with fighters (can also be beam fighters), scramble them once the enemy enters the system. If the station is heavily armored, you can drop it on the jump point so you can attack while the enemy suffers jump shock, or you can build them cheaper and put them further away. The real bonus is you can change the fighters with newer fighters even without towing them back home.
In general, while sensor stations can always be worth using, defense stations are useful only if you think a jump point is likely to be a zone of conflict, because you cannot defend EVERY jump point well. If you have multiple ways an enemy can get inside your important systems, it's better to build a mobile fleet + sensor stations for early warning.